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Rinnai RH180 or 100 Gallon Atmospheric?

Good evening Wallies,

Have a client with a 100 gallon eighteen year old atmospheric conventional water heater. He likes good quality new products. His kids have been complaining of not enough hot water. Capacity is needed as he drilled the restrictor out of the shower heads and likes to run as much dhw as desired.

On demand tanks are not going to work in his application for multiple reasons.

Before considering the Rinnai RH180 I offered a 75 gallon 75mbh atmospheric turned to the hottest setting with a asse1017 mixing valve.

Please post thoughts.


  • icesailoricesailor Member Posts: 7,265
    More hot water:

    Raising the temperature of a water heater tank is the same as (theoretically) using a larger model tank. Install a high quality mixer like the Honeywell direct connect mixer with checks and a recirc. port. If you're serious, I will get you the model number. It direct connects to the top of water heaters. The first time I saw one as a demo, I started installing them on all water heaters. You can run the tank at 135*-140*'s and mix down to 120 degrees.

    If your friend is running well pumps or street pressure at 60#, he is wasting water by taking the flow restrictors out. Especially if the bath/showers are on the first floor. There are many shower heads sold today with flow restrictors in them that you can not tell the difference. If it is a 30/50# pump setting, you probably need to remove them on the second floor.

    If they are filling bath tubs, don't fill with hot water only and then temper it with cold. You run out of hot water faster. Temper the water for comfort, then add cold. If you fill a bathtub with 106 degree water, you can get scalded and suffer from Hyperthermia. If your body temperature goes to 106, it is EMT time and they put you in a tub of ice. So you don't die.

    I can't imagine any way a 100 gallon 75,000 BTU gas water heater can run out of hot water in a normal house unless they have jetted tubs and use them continuously. If he's running a 75 gallon out, I'd be trying to figure out why.
  • NYplumberNYplumber Member Posts: 482
    edited February 2014

    Thanks for the reply.

    Many of my clients have large homes, this is another. How they spend their money is their choice. If they want to flush it down the drain through the use of many shower sprays or washing machine loads, so be it.

    Im interested in the model number for the mixer.

    I assume they run low on water due to the current tank being old. The dip tube is probably partially cracked and the bottom is most likely heavily scaled causing insulation between the burner and water.

    75 gallon 75k, .7 energy factor

    First hour 100 degree rise


    100 gallon 75k burner, .7 energy factor

    First hour 100 degree rise


    Rh180 90k burner, .80 energy factor

    First hour 100 degree rise


    Any calculation to calculate the first hour rating with 125*f outlet from the mixing valve and 140f* (or higher) storage temperature?

    Edited RH180 specs.
  • icesailoricesailor Member Posts: 7,265
    edited February 2014
    All Mixed Up:

    Here's a link to Honeywell and a PDF showing the different ones. Go down the pages. It is a AMX102-us-1LF, meaning that it is 1". You can get it soldered or threaded. The "1LF" means it is a 1" valve and is lead free. It has a maximum of a 20 GPM flow rate.

    Here's another cut:

    I don't know the circumstances you have but I find it really unusual to be running out of how water with a 100 gallon water heater. You could have a cross flow problem that you haven't noticed or know about. If they have the old Moen single lever PULL OUT shower valves, the balancing spool piston may be sticking, or the checks are bad. If you walk into a bathroom and turn on a lav faucet and you hear a "click" behind the shower valve, the checks are bad. Even the newer-old Moentrol valves had the cross connection outside the shut-off. That's why they needed the checks. The bigger the house and the more bathrooms, the greater the opportunity for a cross connection.

    There may be some information somewhere as to how much of a flow volume increase you will get. Its been my experience in the real world that the figures are printed on the rolls of those jumbo packs of toilet paper sold at Costco and Wal-Mart. They can't take into consideration, human use of the products.

    Wealthy people are funny as to what their priorities are for spending money. They can have a toilet in the main "powder room" (for guests a cocktail hour) that flushes so badly, there is a plunger behind the pedestal sink and a toilet auger in the closet. So they don't have to call you as often. They have a mold stained North facing roof that where the sun doesn't shine is all black. The front side where the sun shines is fine for a 7 year old roof with a 30 year warranty. But a roofer comes along and tells then they need a complete new roof with a 30 year warranty against staining.

    You tell Biff (the husband) to change the toilet to one that reliably flushes and save the embarrassment of guests stopping up the toilet. ($400.00?) Biff says NO, too expensive. While 6 Amigo's from Jose's Lawn and Landscaping services is mowing the lawn and picking weeds while a couple of Senoritas are deadheading the flowers in the beds.

    Muffie (the wife) is at Cocktails where Winky tells her of this WONDERFUL toilet she had installed that is a Kohler Cimmeron with a "Comfort Height" so it is easier to sit on because of her need for a hip replacement. Muffie tells Biff, they both run down to Home Depot and get one on sale. And call you up to install it.

    They'll spend money on what they want.

    At least that has been my experience.
  • JackJack Member Posts: 936
    Wrong specs on the RH180

    The RH180 has a 90,000 btu tankless on the 40 gallon tank. This is a "Hybrid" tank/tankless unit. There are a few things to understand about it. Unlike a true tankless where temperature is guaranteed at the expense of pressure, when flow rates exceed the ability of the 180 or 199 kbtu burner to deliver hot water, The RH180 is a different animal. The cold water supply is fed to the tank. The built in a-stat and pump will make on cold water introduction to the tank and run until the stat is satisfied. At 3 gallons or less of flow it will make hot water all day long, but it is a tank and if you have a high flow rate, (6gpm,10gpm?) you can deplete the hot water just like in a standard hot water heater. You will have higher recovery though because of the 90kbtu burner. Also, unlike any other Rinnai water heater, all of which are sealed combustion, on the RH180 you have to pay attention to combustion air requirements as it is a Cat I appliance.
  • IronmanIronman Member Posts: 3,421
    Load calculation

    You need to do a domestic load calculation. Neither you or your customer will be happy if he spends a chunk of money on something that doesn't meet his needs. Don't guess at it.

    Use a 5 gal. bucket to time the flow rate of each fixture since you don't know that with the orifices drilled out.

    Then, get with your rep and let them size it if you don't have a program or know the formulas. Ask your customer how many fixtures, particularly showers, he expects to run at the same time.

    From what your describing, it looks like he may need two tankless (at least) twinned together.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • RobGRobG Member Posts: 1,850

       How about manifolding multiple tankless units (I don't know what their GPM requirements are)? I have heard good things about the Eternal's as they have a built in tank to prevent the "cold sandwich". You can manifold the PVC venting so you only have one exhaust penetration, intake can come from inside or outside. Caveat, I have never used this brand so my opinion is based on hearsay. Most, if not all manufacturers at this point have the capacity to cascade multiple units to provide whatever GPM required.

  • RobGRobG Member Posts: 1,850
    Great minds

    Great minds think alike!
  • NYplumberNYplumber Member Posts: 482

    Yes I stand corrected, first hour is 149.56 based on a 100*f rise. I had thought the btu was 180 due to the name RH180.

    This is a game changer.
  • NYplumberNYplumber Member Posts: 482

    As stated in the original post, a straight tankless wont due for reasons I wont discuss here. The 100 gallon tank with a mixer is looking better and better when looking at cost vs run cost vs maintenance. I may be able to put a high powered Noritz on the wall and connect it to a large ss or glass lined storage tank. Will present the options to the client and see what turns out.
  • RobGRobG Member Posts: 1,850
    edited February 2014
    I don't understand?

    I don't understand? Why can't you discuss the use of a tankless water heater?

    The rinnai 180 is just a tankless water heater connected to a tank. 

  • NYplumberNYplumber Member Posts: 482

    Tankless tied to a tank is fine. Tankless on its own not fine. Just take it as that, or feel free to contact me off line to discuss.

    Regardless need dump load, so a tank and tankless would be great.
  • icesailoricesailor Member Posts: 7,265
    Tankless Gas:

    Because with a straight tankless works great on continuous flow? But every time you shut off a faucet for a moment, the stoppage in flow shuts tha burner, the system goes into Post Purge, Stops, goes into pre-purge, lights off, and then starts heating the flowing water? That scream from the upstairs Master Bath is the woman of the house getting a blast of cold water on her while she is trying to get the soap out of her hair.

    Is that what you mean?

    That doesn't happen with Buffer Tanks.
  • NYplumberNYplumber Member Posts: 482

    Totally off target icesailor. Feel free to contact me.

    Btw thanks for telling me about the direct fit mixing valve. Used it on a 50 gallon yesterday where a high recovery was needed but didnt fit due to an extremely small mechanical room.
  • RichRich Member Posts: 2,224

    Check the Neighborhood for webinar on circulators and indirect tanks . Doesn't sound like what you want but it is . All the calcs you are looking for are in there .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC 732-751-1560
    Serving most of New Jersey , Eastern Pa .
    Consultation , Design & Installation
    Rich McGrath 732-581-3833
  • Larry WeingartenLarry Weingarten Member Posts: 1,173
    Is there any chance...

    ... your client would consider one or multiple shower heat exchangers to make life easier on the heat maker?

    Yours,  Larry
  • NYplumberNYplumber Member Posts: 482

    Good morning Larry W,

    Unsure what shower heat exchangers are.
  • icesailoricesailor Member Posts: 7,265

    You're on a Carousel.

    What is the temperature of the water in the system that you are running?

    Do you have thermostatic mixers? You DO have single lever pressure balance shower valves. I'm sure they are code where you are.

    Before you commit to some overly complicated and expensive solution, turn up the temperature in the existing water heater and see if they still run out of hot water.

    Energy regulations require lower tank temperatures. Thermostatic shower mixers will not ever work properly with 120 degree water. Some I have installed call for 140 degree water to mix properly. Single lever Pressure Balance valves can be difficult with low hot water temperature because they can't slow the cold down enough to get a decent mix. If you have to turn the lever all the way to hot without the limit stop, the valve isn't getting enough hot water. What's the temperature coming out of the water heater? What is it going into valves? If it is more than a 15 degree (I'd almost say 10 degrees), you might have a cross connection. All I'm suggesting is for you to not get caught with your shorts in the wrong place.

    It takes a lot of nuts (BTU's) to make a lot of hot water quickly, or a lot of hot water stored slowly. Or both. It depends on what someone is willing to spend.

    My hot water is fine.
  • RobGRobG Member Posts: 1,850
    Reverse indirect?

    If the customer has hot water heat and needs a consistent dump load, you should consider a reverse indirect. Properly sized, it will give endless hot water without the pressure drop of a tankless.

  • Larry WeingartenLarry Weingarten Member Posts: 1,173
    Here are some links...

    ... to different makers of shower heat exchangers.  Done right, it's a way to need about half the hot water generating capacity.   I'm not sure GFX is still up and running, but it was the first one. 

    Yours,  Larry
  • NYplumberNYplumber Member Posts: 482

    Current tank is already jacked up on the thermostat by the home owner. He put the job on hold till he decides what he wants.
  • NYplumberNYplumber Member Posts: 482

    To date haven't been happy with these. Actually ended up taking a few out and installing oversized indirects to handle dump load and large first hour ratings.
  • NYplumberNYplumber Member Posts: 482
    Rinnai plus storage

    Just wanted to chime in. Installed a Rinnai RU98i and a storage tank for a restaurant yesterday. Set up the system so that even if the storage tank is cold, so long as the draw out of a faucet, sprayer or appliance is under what the tankless can supply, they get the hot water from the tankless and not the cold from the tank.

    The employees of the restaurant were utterly surprised how the storage tank was full of cold water from filling the system, yet two minutes later they were getting steaming water at the sink sprayers. Job turned out real nice.
  • icesailoricesailor Member Posts: 7,265
    Instantaneous heaters and tanks:

    I did the same thing on a job. It worked out really well.

    Mine has "issues" with the municipal water system that kept sending black bits of something growing in their pipes that would get stuck in the inlet strainer of the Rannnai. I put a Cuno Stainless Steel filter that could handle hot water and not melt.

    If it slows down, check that filter in the inlet. It isn't much and it takes very little to slow the flow and keep it off high fire.
  • SWEISWEI Member Posts: 7,356
    Glad it worked out

    I'm curious about the piping layout you used to accomplish the switching.

  • NYplumberNYplumber Member Posts: 482

    Thanks for the tip. There is a filter on the main that one of the employees changes regularly. I have room on the piping to add a filter if necessary.
  • NYplumberNYplumber Member Posts: 482

    Will email you some closeups when I return to the job site shortly.
  • heatpro02920heatpro02920 Member Posts: 991
    also curious

    I would like to see how that is piped also..

    on another note, I have never heard of any house running a 100ga heater out!!! that is insane amounts of water...

    I did a plating companies water heater, they would use HUGE amounts of hot water when washing these blankets that were used in their plating process... They had 4- 3/4" hoses spraying these blankets down and the water had to stay above 135 degrees... They had a 2" main so water was plentiful, BUT even with each hose on its own commercial 100ga tank, they would not have hot water long enough to get the job done...

    So I walk into this after they have already had multiple companies there, tried multiple tanks and heaters...

    Money is barely an object because when these blankets take to long to clean they get ruined and I was told they are very expensive... So Im not sure if the other contractors were told "money is not an object" or not, but I had bought a used/new {3 months old} Utica JD700.

    I took that jd boiler and paired it with 2 TT smart 80's and they have enough hot water to wash down a small city....

    So obviously your customer doesn't need that much, BUT I would say if they don't care about running a 100ga direct, maybe a properly sized boiler and an indirect would be the best bet, I would perform a few tests to find out how much water they actually need, then pick a smart tank to match, then pick a boiler to match that.... It wont be cheap, but they will never run out of hot water again.. And when you compare this option to a direct fired unit that will make the similar amounts of water it will end up just slightly more and last longer...

    You can always contact ao smith, once you have some real numbers of how much hot water they need, they will tell you exactly what your options are, they built one of my customers a custom 2200 gallon tank, so I am sure they will have an option for you...

    Although the best option would be to not use so much water, I have 4 full bathrooms in my house an RU98 and I never run low on hot water, we have had 4 showers going at once and no complaints... {High sierra shower heads}....
  • SWEISWEI Member Posts: 7,356
    Indirect with dedicated boiler

    hard to beat those recovery rates.  I've done a couple of commercial jobs pairing a 399k mod/con with a SMART 120 which have worked out quite well.  Not fun moving those monsters, maybe dual 80's would be worth a try...
  • NYplumberNYplumber Member Posts: 482
    edited March 2014

    Not too hard to believe when large homes are used and many children take long showers, washing machine loads, and running sinks simultaneously.

    A client with an eighty gallon indirect and large btu boiler complained last week of running low so I went over to test. Rain shower, ran a bath, used a sink, etc and after an hour it started running warm. Tank is kept at 160 and has a mixing valve to temper. Of course I over exhausted the system intentionally.

    On another note, four showers on a RU98 at once? What temp is the dt across the hx and what flow from the shower heads? Thats surely not high flow heads.
  • heatpro02920heatpro02920 Member Posts: 991
    Thats just a lot of hot water

    at my house I can indeed run 4 showers at once, 115* set on the rinnai, incoming varies in new england... but the delta is most likely around 65, 4 high sierra heads with valves on full hot, no issues at all...

    I hate spending money to heat water so I try to keep it as efficient as possible, I have done a lot of high quantity water heating systems and I try to keep energy rite up there with comfort, you start doing the math and seeing how much your daughters hour long shower costs you and you will be installing valves on the outside wall with timers on them, lol... We have a 15 minute rule at my house, propane was just over $5 a gallon!!!!
  • NYplumberNYplumber Member Posts: 482

    The high end clients wont settle for anything under 4-5 gpm! They want to feel it pour! Some have so much water the drain cant handle it. Some have truff drains with 2inch drain pipe.

    One client has three shower bodies in one shower. Another shower I did used the 24in Kohler shower tile.

    How often do they need all the water at once? Infrequent to frequent depending on the home. Same goes to their high end four door sports cars with close to 500hp from the factory. How often do they use it? Less often then they use all the hot water up.
  • icesailoricesailor Member Posts: 7,265
    Old Money Vs. New Money


    Does this happen with ALL your customers or just one?

    I don't question anything you have said. But if they want 4-5 GPM's in their shower heads, first off, it's illegal for shower heads to deliver that amount (who's enforcing it) but it is also 240 to 300 GPH out of a water heater. That water is no more than 105 at the shower head so you need one large amount of cold water to mix with even 140 degree hot water. If you take a tank type 100 Gallon gas water heater with a high output and add the first hour rise/total, that's one heck of a lot of hot water. If ALL your customers have that problem, that is one thing. But if it is just one customer, I'd be seriously be looking into a hot water cross connection somewhere. They are insidious and hard to find. I think that someone is jerking you around. I defy anyone, ANYWHERE to stand in a shower without a flow restrictor in the head, with 60# PSIG to the valve, the valve working properly, and stay there for more than 5 minutes without turning down the volume. It HURTS badly. Then, over ride the limit stops on the shower valve and let it run to 110 degrees. They will be scalded and be turning down the temperature faster than that New York Minute they used to brag about.

    I have worked for a lot like your customer(s). If they are old money, and they needed more hot water than the normal water heater could provide because too many showers were using it all up, they would have told the children to space out their showers and cut down on the time. If they didn't, they would be calling you about timers for the children's showers. The parents are different. They're "careful" with their money. We might call them cheap.

    New money, they usually want the best but aren't willing to pay for it, once they find out how much it costs. Their cheaper but more demanding for a cheap fix.

    You really might need to look into a cross connection.

    Someone here (Mark E?) had a problem similar and after a while, found out it was cross connections in some shower valves. If you have some of those high end thermostatic mixer shower valves like Dornbracht or others, the thermostatic mixers go bad and need to be replaced. I can't remember the brand off hand but their factory in Germany burned down and they lost all their patterns. If they are that type of valve, there are no parts and the valves must be replaced.

    I've worked on Hotels, large and small restaurants, Guest Houses and institutional buildings like a Nursing home. I've never heard of such hot water dilemma's a private residence.

    I replaced a 100 Gal oil fired water heater with a Bock 73E 70 gallon oil fired water heater (220 GPH first hour recovery at 100 degree rise) in a social club that had a restaurant and dorms. The only time it ran out of hot water was around 10 O'clock PM, they would take the rubber mats outside and wash them. The kitchen was closing down and they were washing up. They weren't supposed to do this but there was a Moen mixer shower valve, set so the couldn't get hot water. Someone by-passed it and they were getting direct hot water. Shutting down the hot to the valve stopped the foolishness.

    There's a solution.
  • heatpro02920heatpro02920 Member Posts: 991

    want what they want. I have a few "Money is no object" customers, but I still push them towards efficiency...

    I installed 4 RU98's in a house last summer, with a Rheem Marathon 15ga electric water heater for his recirc system {almost $1000 my cost just for the grundfos timer/stat pump and marathon tank!!!} The install came really nice, easily the most expensive residential DHW install I have done to date, they were rack mounted {Rinnai sells racks} in the center of the house, vented up through the chimney, controls in the laundry kitchen and a couple baths, HUGE gas line, had to submit plans for the system because of the amount of BTU's, ect job was a giant pain, but Rinnai sells everything to make it easy...

    Anyway, the house had 4 full baths and a 2 halfs, BUT ONLY 2 people living there, lol 1 ru98 would have done more than what they needed, but instead they spent over 12K on DHW, and wouldnt agree to a geothermal system, figure that out...
  • icesailoricesailor Member Posts: 7,265
    Geothermal DHW:

    What they spent on the DHW you installed is chump change compared to what they could have paid for a working Geothermal system, once it was fully up and running.

    Then, cones the service and problems with the water quality.

  • heatpro02920heatpro02920 Member Posts: 991
    edited March 2014

    I installed radiant heat with back up 90+ furnaces in the ac duct work, and a pair of buderus gb's... When factoring in the entire system for a little more they could have went geo..

    I haven't had any water quality {DHW} problems with any geo systems I have installed, closed loop works very well and they would be saving huge amounts every year in energy bills...

    As far as service problems go, the new equipment is reliable, the pump and dump systems gave geo a bad taste for some, but the stuff available now is reliable and long lasting... as with anything else the installer is the wild card, you install it correctly and you wont have any issues....

    I don't see the extra comfort in dumping tons of water down the drain when taking a shower, to each their own, but I see all that extra water as more energy to pump it and heat it, more wear and tear on my well system, septic system, plumbing, and water heater... Just doesn't make sense, in my house I have a single RU98 {used to have 2} and a Hybrid 50 ga tank, I am going to use the hybrid during the summer and I use the tankless during the winter. This will be the first year I use the hybrid... I also have a bosch mini tank that supplies my recirc loop... Now if I had to pay for someone to install all of that equipment I would not have had it installed, I would have went wit ha std single rinnai unit {non condensing}...
  • NYplumberNYplumber Member Posts: 482

    Its a blend of old and new money. They're careful how they spend it, but when they want something (hot water) and they trust in you to deliver it, they don't mind spending

    I have had homes with water blending in the walls, thankfully its not the norm. Sometimes its a bad check valve on the cold inlet to the heater and the recirc pump is the issue. Other times it has been thermostatics. I am actually going back to a home that was plagued with bad thermostatic check valves to pull apart another shower trim for inspection. The equipment is a 399mbh boiler and 119 gal dhw tank.
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